When workpieces with closed curves are to be ground, until now the workpieces have been ground by area and then rechucked in a different position in a workpiece holder. For every subsequent indexing position another nominal profile segment is laid on the projection screen, care being taken that the workpiece is reindexed in such a manner that its image is brought into correspondence with the nominal profile line laid on the projection screen. A prerequisite for the latter condition is that the nominal profile lines be drawn on the nominal profile drawing in the position of the subsequent indexing in such a manner that they always lie contiguous to one another as a result of reindexing of the workpiece.
This procedure is extraordinarily time-consuming, and it also entails the risk of errors arising due to rechucking.
The invention is based on the problem of improving a projection profile-grinding machine of this type in such a way that even closed curves may be ground into workpieces with little expense and great precision.
This problem is solved according to the invention in an optical projection profile-grinding machine of the type described at the outset by means of the features of the workpiece and the projection screen with its nominal profile line being capable of rotation about the optical axis of the projector, fixation in different angular positions, and rotation in synchrony and at the same angular velocity.
Thus, according to the mechanism, both the workpiece and the projection screen and nominal profile line carrier are arranged such that they rotate about the optical axis of the projector, and both workpiece and nominal profile line are rotated in synchronism at the same angular velocity.
The rotation can occur in large intervals, so that one area of the workpiece is ground at a time and when this area is finished workpiece and nominal profile line are rotated by a certain angle so that thereupon a new area can be machined.
It is also possible to carry out the rotation in very small steps that follow one another in quick succession. This is advantageous, for example, when a body is to be ground into a circular cylindrical form with a grinding wheel executing an oscillating stroke movement parallel to the optical axis. This method of operation ensures that the grinding wheel is always introduced to the workpiece in a radial direction.
This method of operation is particularly advantageous when conical grinding of the workpiece is desired. The latter may be achieved simply with this method of operation by effecting the oscillating stroke motion of the grinding wheel not exactly parallel to the optical axis of the projector, but at an angle corresponding to the desired conical form.
By way of example, slight rotation of the workpiece and nominal profile line can be executed after each stroke of the grinding wheel in a grinding process, the distance of the grinding wheel carrier from the optical axis remaining constant throughout the entire rotation.
It is advantageous for the rotational drive for the workpiece and the rotational drive for the projection screen and the carrier to be coupled to each other by gearing. In this way synchronous rotation of the workpiece and the nominal profile line at the same angular velocity is ensured in a simple manner.
It is particularly advantageous for the rotational drives for the workpiece and the projector and carrier to consist of servomotors which are actuated in synchronism by a numerical control system. This numerical control system can simultaneously control the delivery of the grinding wheel in the direction toward the workpiece, so that, in all, fully automatic machining is ensured, which may be followed on the projection screen.